Chronic rejection, which remains the most important challenge to the long-term survival and quality of life of lung allograft recipients, is manifested by bronchiolitis obliterans (BO), a fibroproliferative disorder involving the narrowing or obliteration of bronchiolar lumens by scar tissue, with resultant impedance to airflow. Currently, there are no therapeutic interventions, including immunosuppression, that have proven to be of major clinical benefit. Pirfenidone is an anti-fibrotic agent that is effective in blocking the development of fibroproliferative disorders, including clinical idiopathic pulmonary fibrosis. Moreover, this drug is well tolerated clinically, with only minor adverse effects and no significant toxic effects. Although pirfenidone is not known to have immunosuppressive properties, it does alter expression of inflammatory and profibrotic cytokines and alter the incidence of immune-mediated injury in models of multiple sclerosis and asthma. Most importantly, we have found that pirfenidone attenuated chronic airway obstructive lesions in a mouse tracheal transplant model, and reduced both acute cellular rejection and the development of fibrosis in a rat lung transplant model. We now propose to evaluate the mechanisms involved in pirfenidone's graft-protective effects. Our first hypothesis is that pirfenidone reduces transplant-mediated injury and rejection by reducing the production of proinflammatory and profibrotic cytokines and the associated recruitment of host inflammatory cells. We plan to study short- and long-term effects of pirfenidone on lung function and histology. In addition, we will characterize the immune and cytokine response of rat lung allografts receiving pirfenidone treatment, using multi-parameter Luminex and/or ELISA tests to determine BAL and lung levels of Th1 (IFN-?, TNF-?, IL-2, IL-12), Th2 (IL-4, IL-10, IL-13), and Th3 (TGF-[unreadable]) cytokines, and expression of the adhesion molecule, ICAM-1. Our second hypothesis is that pirfenidone may also directly block lymphocyte activation and proliferation. This will be evaluated in vitro and in vivo, using state-of-the art methods that will collectively generate a composite and detailed body of work that for the first time will assess direct immune effects of pirfenidone on host CD4 and CD8 T cells. Lastly we believe that pirfenidone has direct effects on the numbers and/or functions of host naturally occurring Foxp3+ Treg cell, thereby contributing to the enhanced survival of rat lung allografts. We will therefore evaluate the effects of pirfenidone on the generation and suppressive activities of host Treg cells in vitro and in vivo. Long term survival for lung transplantation is relatively poor since acute and chronic rejection occurs in the majority of patients. Our preliminary data identified that pirfenidone has protective effects against both acute and chronic rejection in a rat model of lung transplantation. This proposal will further evaluate its potential in promoting long term survival of lung transplants and the mechanisms of its protective effects. [unreadable] [unreadable] [unreadable]